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Abstract:

In a non-limiting and example embodiment, a method is provided for
arranging multi-channel wireless communications, including detecting, by
a communications apparatus, information on available bandwidth for a
transmission opportunity applying multiple channels, and controlling
duration of channel occupancy for at least one of channels available for
the transmission opportunity on the basis of the information on available
bandwidth.

Claims:

1. A method, comprising: detecting, by a communications apparatus,
information on available bandwidth for a transmission opportunity
applying multiple channels, and controlling duration of channel occupancy
for at least one of channels available for the transmission opportunity
on the basis of the information on available bandwidth.

2. The method of claim 1, wherein a duration of medium occupancy within
the transmission opportunity and/or a time limit for the transmission
opportunity is calculated for at least one of the available channels on
the basis of the information on available bandwidth.

3. The method of claim 1, wherein the apparatus is provided with access
to a set of predetermined transmission opportunity limit parameters,
further comprising defining, for each available secondary channel, a
transmission opportunity limit value on the basis of the transmission
opportunity limit parameters and the information on available bandwidth.

4. The method of claim 3, wherein the set of predetermined transmission
opportunity limit parameters comprises at least one bandwidth-specific
factor for determining a transmission opportunity limit value for at
least one secondary channel on the basis of a transmission opportunity
limit value for a primary channel.

5. The method of claim 3, wherein the set of predetermined transmission
opportunity limit parameters is received from another device in at least
one of a probe response and a beacon message.

6. The method of claim 3, wherein the communications apparatus determines
the transmission opportunity limit for each of the secondary channels
available for the transmission opportunity on the basis of the set of
predetermined transmission opportunity limit parameters and a
transmission opportunity limit of the primary channel, estimates the
total duration of channel occupancy during the transmission opportunity,
and ensures for each of the channels that the channel occupancy does not
exceed the transmission opportunity limit determined for the channel.

7. The method of claim 6, wherein the occupancy of the primary channel
and the occupancy of at least one secondary channel are defined on the
basis of separate timers during the transmission opportunity, the
duration of the primary channel occupancy is prevented to exceed the
transmission opportunity limit set for the primary channel, and the
duration of the at least one secondary channel occupancy is prevented to
exceed the transmission opportunity limit set for the at least one
secondary channel.

8. The method of claim 1, wherein a bandwidth increment factor is
generated on the basis of ratio of available bandwidth and the bandwidth
of the primary channel, and a transmission opportunity limit is
calculated for at least one secondary channel on the basis of a
transmission opportunity limit of the primary channel and the bandwidth
increment factor.

9. The method of claim 1, wherein expected duration of the transmission
opportunity is calculated on the basis of the available bandwidth, and
the calculated duration of the transmission opportunity is included in a
duration field of a request to send message.

10. An apparatus, comprising at least one processor; and at least one
memory including computer program code, the at least one memory and the
computer program code being configured to, with the at least one
processor, cause the apparatus at least to: retrieve or calculate a set
of predetermined transmission opportunity limit parameters, each
associated with specific bandwidth, and transmit at least some of the
predetermined transmission opportunity limit parameters to a radio
device.

11. The apparatus of claim 10, wherein the set of predetermined
transmission opportunity limit parameters comprises at least one
bandwidth-specific factor for determining a transmission opportunity
limit value for at least one secondary channel on the basis of a
transmission opportunity limit value for a primary channel.

12. The apparatus of claim 10, wherein the apparatus is a wireless local
area network access point and configured to include an information
element comprising the at least some of the transmission opportunity
limit parameters in an IEEE 802.11 beacon frame or a probe response
frame.

13. An apparatus, comprising: at least one processor; and at least one
memory including computer program code, the at least one memory and the
computer program code configured to, with the at least one processor,
cause the apparatus at least to perform: detect information on available
bandwidth for a transmission opportunity applying multiple channels, and
control duration of channel occupancy for at least one of channels
available for the transmission opportunity on the basis of the
information on available bandwidth.

14. (canceled)

15. The apparatus of claim 13, wherein the apparatus is configured to
access a set of predetermined transmission opportunity limit parameters,
and the apparatus is configured to define, for each available secondary
channel, a transmission opportunity limit value on the basis of the
transmission opportunity limit parameters and the information on
available bandwidth.

16. The apparatus of claim 15, wherein the set of predetermined
transmission opportunity limit parameters comprises at least one
bandwidth-specific factor, and the apparatus is configured to determine a
transmission opportunity limit value for at least one secondary channel
on the basis of the factor and a transmission opportunity limit value for
a primary channel.

17. The apparatus of claim 15, wherein the apparatus is configured to
receive the set of predetermined transmission opportunity limit
parameters from another device in at least one of a probe response and a
beacon message.

18. The apparatus of claim 15, wherein the apparatus is configured to
determine the transmission opportunity limit for each of the secondary
channels available for the transmission opportunity on the basis of the
set of predetermined transmission opportunity limit parameters and a
transmission opportunity limit of the primary channel, the apparatus is
configured to estimate the total duration of channel occupancy during the
transmission opportunity, and the apparatus is configured to ensure for
each of the channels that the channel occupancy does not exceed the
transmission opportunity limit determined for the channel.

19. The apparatus of claim 18, wherein the apparatus is configured to
define the occupancy of the primary channel and the occupancy of at least
one secondary channel on the basis of separate timers during the
transmission opportunity, the apparatus is configured to prevent the
duration of the primary channel occupancy to exceed the transmission
opportunity limit set for the primary channel, and the apparatus is
configured to prevent the duration of the at least one secondary channel
occupancy to exceed the transmission opportunity limit set for the at
least one secondary channel.

20. The apparatus of claim 13, wherein the apparatus is configured to
generate a bandwidth increment factor on the basis of ratio of available
bandwidth and the bandwidth of the primary channel, and the apparatus is
configured to calculate a transmission opportunity limit for at least one
secondary channel on the basis of a transmission opportunity limit of the
primary channel and the bandwidth increment factor.

21. The apparatus of claim 13, wherein the apparatus is configured to
calculate expected duration of the transmission opportunity on the basis
of the available bandwidth, and the calculated duration of the
transmission opportunity is included in a duration field of a request to
send message.

22. The apparatus of claim 13, wherein the apparatus is a communications
device comprising a transceiver for communicating according to an IEEE
802.11ac standard, and the channels are IEEE 802.11ac channels.

23. A computer readable storage medium comprising one or more sequences
of one or more instructions which, when executed by one or more
processors of an apparatus, cause the apparatus to perform: detect, by a
communications apparatus, information on available bandwidth for a
transmission opportunity applying multiple channels, and control duration
of channel occupancy for at least one of channels available for the
transmission opportunity on the basis of the information on available
bandwidth.

Description:

FIELD

[0001] The non-limiting example embodiments of this invention relate
generally to arranging access to wireless medium, and more specifically
to arranging wireless medium access in wireless networks with
multi-channel capabilities.

BACKGROUND

[0002] Various techniques exist for wireless networks to differentiate
between data flows having different quality of service (QoS). For
example, medium access control (MAC) layer may be provided with
techniques to prioritize wireless medium access for delay-sensitive
traffic. Some wireless communications technologies enable to selectively
use one or more radio channels to vary data transmission rate.

SUMMARY

[0003] Various aspects of examples of the invention are set out in the
claims.

[0004] According to a first embodiment, there is provided a method,
comprising: detecting, by a communications apparatus, information on
available bandwidth for a transmission opportunity applying multiple
channels, and controlling duration of channel occupancy for at least one
of channels available for the transmission opportunity on the basis of
the information on available bandwidth.

[0005] According to a second embodiment, there is provided an apparatus
comprising at least one processor and at least one memory including
computer program code, the at least one memory and the computer program
code configured to, with the at least one processor, cause the apparatus
at least to: detect information on available bandwidth for a transmission
opportunity applying multiple channels, and control duration of channel
occupancy for at least one of channels available for the transmission
opportunity on the basis of the information on available bandwidth.

[0006] The invention and various embodiments of the invention provide
several advantages, which will become apparent from the detailed
description below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] For a more complete understanding of example embodiments of the
present invention, reference is now made to the following descriptions
taken in connection with the accompanying drawings in which:

[0024]FIG. 1 illustrates an example of a wireless communication system
including elements contending for network resources, such as elements
supporting IEEE 802.11 features. However, it will be appreciated that the
application of the present features is not limited to any specific
network type(s), such as IEEE 802.11 based networks. It may be applied to
other current or future networks, in which the transmission between two
entities may be carried on one or more secondary channels in addition to
a primary channel.

[0025] Wireless devices 10, 30 may associate with an access point (AP) or
base station. In some embodiments, the devices 10, 30 are IEEE 802.11
WLAN stations (STA). In one embodiment the wireless device 10, 30 is
capable of operating as a mesh node, such as a mesh node operative
according to IEEE 802.11s. In a further example embodiment the wireless
device 10, 30 is capable to operate 18 in independent BSS (IBSS), and
operate according to principles of IBSS network, whereby no AP 20 is
involved.

[0026] The wireless device 10 may be capable of communicating via zero or
more secondary channels 14, 16 in addition to a primary channel 12
defined for the device 10. In IEEE 802.11 based WLAN, a primary channel
is a frequency channel in which a WLAN STA performs contention-based
access to the wireless medium and in which it may receive transmissions.
In some embodiments the device 10 is capable of operating under
multi-channel features being developed by the IEEE 802.11ac working
group. Channel bandwidths between 20 MHz (single channel) to 160 MHz are
currently being discussed. However, it will be appreciated that the
present features may be applied in connection with other multi-channel
access techniques.

[0027] The basic 802.11 MAC layer uses the distributed coordination
function (DCF) to share the medium between multiple stations 10, 30. The
DCF relies on carrier sense multiple access with collision avoidance
(CSMA/CA) and handshaking with request to send (RTS) and clear to send
(CTS) frames to share the medium between stations. However, the DCF does
not result in a mechanism to differentiate the channel access rules
between stations or their traffic.

[0028] The IEEE 802.11e is an extension of the IEEE 802.11 to provide
Quality of Service (QoS) for applications requiring real-time services.
It is divided into two parts: Enhanced distributed channel access (EDCA)
and hybrid coordination function controlled channel access (HCCA). In
EDCA there are eight traffic categories (TC) that are mapped to four
access categories (AC). Each AC has its own transmission queue. A station
with high priority traffic waits a little less before it sends its
packet, on average, than a station with low priority traffic. The concept
of transmission opportunities (TXOPs) was introduced in the 802.11e
amendment to increase the transmission efficiency of the traffic
belonging to the same AC. A TXOP is a bounded time interval in which a
STA that has obtained the TXOP, i.e. a TXOP holder, maintains the right
to transmit data, control, and management frames of a particular AC so
long as the duration of frame sequence does not exceed the TXOP limit of
that AC. During EDCA, an EDCA parameter set determines the channel
access. The EDCA parameter set creates the differentiation between ACs.
The EDCA parameter set has five parameters: The Access Category
Indicator, The content window (CW) minimum and maximum, the an
arbitration interframe space (AIFS) and the TXOP limit. The TXOP limit
indicates the maximum duration during which the station is allowed to
transmit. The current TXOP limit defines the TXOP limit for legacy
802.11n and 802.11a/g devices, and 802.11ac transmissions to 20 MHz
bandwidth.

[0029] Each STA 10 may be arranged to define TXOPs in its own primary
channel. In the example of FIG. 2, channel 1 represents the primary
channel for a user. A TXOP 202 may begin after AIFS time and a contention
window (CW) period 200 defining the backoff period.

[0030] If at least one secondary channel is idle, the STA may transmit
204a, 204b, 204c on at least one secondary channel (channels 2 to 4) for
wider bandwidth operation to increase data rate. As further illustrated,
(another user) may start a multi-channel transmission in another primary
channel 206 and other secondary channels only after the first
multi-channel transmission. If multiple channels are applied for
transmission in a given TXOP, such TXOP may also be referred to as
multi-channel TXOP.

[0031] The current application of TXOP parameters is however not optimal
for multi-channel operations, such as operations developed for the IEEE
802.11 ac. There is a single TXOP limit specified for an AC, whereby the
TXOP limit will be the same for primary 202 and non-primary (secondary)
204a-c channels for transmitting data of a particular AC. Hence, the TXOP
limit on secondary channels will follow the TXOP limit on the primary
channel. Thus, a TXOP holder capable of using multiple channels may
reserve unnecessarily long TXOPs, resulting in inefficient use of radio
resources.

[0032] According to example embodiments of the invention, and as
illustrated also in FIG. 3, information on bandwidth available for a
multi-channel TXOP is obtained 300. This information may be received on
the basis of results of channel sensing after obtaining a TXOP, for
example. Thus, the information on available bandwidth may be obtained on
the basis of number of channels detected to be idle in the network the
device 10, 30 is associated to. A controller entity managing channel
usage and performing at least the features of FIG. 3 may receive this
information from a lower protocol layer entity, for example.

[0033] Duration of occupancy of at least one of available channels for the
TXOP is controlled 310 on the basis of the information on available
bandwidth. Thus, one or more values for parameter(s) affecting or
defining the duration of channel occupancy may be defined for at least
one of the available channels on the basis of amount of available
bandwidth for the TXOP. Such bandwidth-dependent TXOPparameter value may
be calculated on the basis of input value(s) associated with the
currently available bandwidth, or a value associated with the currently
available bandwidth may be selected amongst a set of predefined values.
The term `transmission opportunity` or TXOP is to be understood broadly
to be initiated by a random channel access operation or at a scheduled
time instance after which messages may be transmitted and received. TXOPs
cover any type of guaranteed or non-guaranteed channel access event,
without limiting the definition only to TXOPs of the IEEE 802.11 based
systems. Although references are made below to IEEE 802.11 based entities
and features, it will be understood that the present features related to
controlling channel occupancy based on available bandwidth may be applied
in other wireless systems.

[0034] A value specifying the expected duration of the TXOP and/or a time
limit for the TXOP may be calculated for at least one of the available
channels on the basis of the information on available bandwidth in block
310. The term `TXOP limit` as applied herewith refers generally to a time
limit parameter specifying the maximum allowed duration of a TXOP, e.g.
similarly to the IEEE 802.11e TXOP Limit parameter. A device may estimate
the expected TXOP duration prior it starts the TXOP. Such expected TXOP
duration value may be sent for other radio devices to indicate the
channel occupancy.

[0035] In case of IEEE 802.11e based WLAN, the TXOP holder maintains
uninterrupted control of the medium during the TXOP. The TXOP holder may
protect the duration that it will maintain the medium occupied for it by
setting the network allocation vector (NAV). The expected TXOP duration
may be included in a duration field of a request to send (RTS) message.
When a CTS message is received for the RTS, the NAV protection is
established on all the channels that carried these messages and the
operation in each specific channel is fully compatible with existing
802.11 systems. In some example embodiments, the elapsed TXOP duration
and the protected duration (NAV) shall be less or equal to the
bandwidth-dependent TXOP limit. The medium occupancy of secondary
channels for the TXOP may be measured separately, and the maximum
duration that these secondary channels may occupied during the TXOP may
be limited by own dedicated TXOP limits. The (maximum) duration of a TXOP
may thus be limited in response to secondary channel(s) being available.
This allows faster release of secondary channels for other primary users
and enables to improve bandwidth usage efficiency.

[0036] Such bandwidth-dependent TXOP parameter values may be specified
separately for each available channel detected to be idle. In alternative
embodiments, a single parameter value calculated based on the currently
available bandwidth is applied for a plurality of available channels.

[0037] A TXOP holder, such as the wireless device 10, which in some
embodiments operates as an IEEE 802.11ac capable non-AP STA, may be
arranged to define bandwidth-dependent TXOP parameter values for each of
the applied channels and control 310 the channel occupancies on the basis
of these TXOP parameter values. In some cases a QoS capable AP 20 may be
arranged to define bandwidth-dependent TXOP parameters and provide them
for TXOP holders.

[0038] Bandwidth-Dependent TXOP Limits

[0039] Further example embodiments for applying bandwidth-dependent TXOP
limits are now further provided. FIG. 4 provides an example of
bandwidth-dependent TXOP limits. One or more 20 MHz channels may be
applied, and a specific TXOP limit is defined for 20 MHz bandwidth 400
(only primary channel is applied), 40 MHz bandwidth 402 (primary and
secondary channel), and 80 MHz bandwidth 404, 406 (also
tertiary/quaternary channel). These bandwidth-specific TXOP limits may
define for each channel the maximum time the channel may be occupied at a
TXOP: The primary channel may be occupied e.g. 3 ms (example value of
TXOPLimit20), the secondary channel may be occupied for 2.25 ms
(=TXOPLimit40), etc.

[0040]FIG. 5 illustrates a method for defining and applying
bandwidth-specific TXOP limit parameters according to an embodiment. The
features may be carried out by a TXOP holder, such as the device 10
operating as an IEEE 802.11ac STA, for example.

[0041] Currently available channels and bandwidth is detected 500. This
block may be entered after receiving channel information from an access
point 20 and in response to a need to initiate a multi-channel
transmission event, for example. In case of 802.11 based transmission,
block 500 may be entered e.g. after detecting a medium free after the
AIFS and CW period. The available channels and bandwidth may be detected
by performing the clear channel assessment (CCA) a point (coordination
function) interframe space (PIFS) before the TXOP obtaining, i.e. the
start of the TXOP. I.e. available channels may be idle channels to which
RTS or data may be sent on the basis of sensing just prior to the TXOP
initiation time. It is to be noted that the device 10 may in connection
of block 500 decide to use only some of available channels and bandwidth,
in which case the "available channel/bandwidth" below may refer to the
channels/bandwidth which the device decides to use.

[0042] Bandwidth-specific TXOP limits, specifying the maximum duration for
a multi-channel TXOP, are defined 510 on the basis of the information on
available total bandwidth. The TXOP limits may be defined separately for
each of the available channels for the TXOP, i.e. for a primary channel
and zero or more secondary channels. For example, the device 10 may have
received and stored bandwidth-specific TXOP limit parameter sets earlier,
and the device 10 may define the TXOP limit values on the basis of the
parameter values retrieved from the memory.

[0043] At least one value for expected TXOP duration may be calculated 520
on the basis of the available bandwidth. It is to be noted that TXOP
durations may be calculated separately for each of the channels. Also the
TXOP limits may be applied in the calculation, to ensure that a TXOP, the
duration of which exceeds the channel-specific maximum values, is not
allocated. At block 520 the device 10 may prepare multiple different
versions of the frames that are going to be transmitted. For instance,
the device may select different traffic to be transmitted by using
different scheduling logics (i.e. to select the recipients and/or the
content, stream or the type of the transmission), apply different
transmission rates for the traffic to be transmitted and aggregate MPDUs
and MSDUs to be transmitted by using different frame aggregation
principles. With these preparations the device may discover the optimal
transmission format for the traffic to be transmitted.

[0044] When the TXOP is started, at least one counter may be activated 530
to measure the duration of the elapsed TXOP, which may also be referred
to as elapsed TXOP duration representing the already used time for the
TXOP. The TXOP duration may be incremented whenever there is an ongoing
transmission, regardless of the transmission bandwidth. However, the
procedure ensures 540 that the bandwidth-specific TXOP limits are not
exceeded. The procedure may ensure in block 540 that duration of the
(total) medium occupancy within the TXOP, which may also be referred to
as total TXOP duration, comprising already elapsed TXOP duration and
estimated remaining TXOP duration, does not exceed the bandwidth-specific
TXOP limit values. The remaining duration indicates the estimated further
required time and may be calculated e.g. on the basis of amount of data
still to be transmitted. For example, if the total TXOP duration reaches
the TXOP limit 404 of FIG. 4 for 80 MHz operations, the transmission may
be performed only on primary and secondary channels and thus by 40 MHz
bandwidth.

[0045] The device 10 may sum the estimated remaining duration with the
elapsed TXOP duration to estimate the total TXOP duration. The device 10
may compare the estimated total TXOP duration value to the TXOP limit
value, and ensure that TXOP limit value is not exceeded. The comparison
of the total TXOP duration value to the TXOP limit values may be
performed at least in the beginning of the TXOP (e.g. when sending the
first RTS) and when estimated total duration is increased or decreased.
Some example triggers for this include: bandwidth is increased or
decreased during a TXOP, or during a TXOP a need to transfer more data is
detected.

[0046] It is to be noted that in case of IEEE 802.11 based WLAN, the total
TXOP duration may include both the elapsed TXOP duration and the NAV
protected future time. The medium occupancy under 802.11 includes both
the time required for transmitting the RTS and the NAV duration. It is
further to be noted that the calculation of (expected) TXOP duration
value may refer to calculation of value for the estimated total TXOP
duration (at the start of a TXOP) or the NAV duration. In case of the
first frame of a TXOP, the NAV value may be equal to the remaining TXOP
duration. Comparison of the total TXOP duration value to a TXOP limit
value may be performed in connection with each RTS/CTS procedure.
However, it is possible that such comparison is performed for each
transmitted frame.

[0047] It is also noted that a remaining duration value, which may be
included in each frame transmitted during the TXOP, may indicate the
remaining time after transmitting the frame. In an example embodiment, in
case a new RTS is sent during an ongoing TXOP, the duration field value
of RTS is updated on the basis of the current situation. Hence, the RTS
duration value may be adapted during the TXOP to be in view of the
current bandwidth situation (more or less bandwidth may be available at
the time of second RTS). The elapsed TXOP duration is not reset. The
updated duration value for the RTS duration field summed with the elapsed
TXOP duration value may not exceed the (channel-specific) TXOP limit.

[0048] It is to be noted that FIG. 5 illustrates only one example of
setting and applying TXOP parameters on the basis of available bandwidth,
and various amendments and additions may be made to this procedure.

[0049] The embodiment of FIG. 5 enables to use both channel-specific TXOP
limits and define TXOP duration(s) on the basis of the available total
bandwidth for the TXOP. In some other examples, only bandwidth-dependent
channel-specific TXOP limits are allocated, or only bandwidth-dependent
TXOP durations are calculated for each of the available channels. In the
latter example variation, each secondary channel may have a different
TXOP duration.

[0050] In case the channels need to be used in a predetermined order, e.g.
the use order may be: primary, secondary, tertiary and quaternary for the
802.11ac, the lengths of TXOP limits should be assigned in the same
order. Thus, the TXOP limit of the channels to be used together with the
earlier channels shall not exceed the TXOP limit(s) of the previous
channels. For instance, transmissions at tertiary and quaternary channels
require transmission also at the primary and the secondary channels, so
the TXOP limit for the tertiary and quaternary channels may be shorter
than the limit for the primary and the secondary.

[0051] FIGS. 6a and 6b illustrate examples of multi-channel operations, in
which the total TXOP durations are limited on the basis of the available
bandwidth. In FIG. 6a both 40 MHz transmissions 60a-c and 80 MHz
transmissions 62 are carried out, and in FIG. 6b 80 MHz transmissions
64a-d occupying all four example channels are applied. It is to be noted
that the variation of the total TXOP durations reflects the load
situation of a STA. As compared e.g. to the example of FIG. 2, when the
80 MHz bandwidth is applied, the total TXOP duration may be shortened,
and the delays for other users accessing the channels can be reduced. The
reduced airtime occupancy will increase the likelihood to capture the
whole 80 MHz bandwidth during contention. This enables to improve the
probability of operating with larger 40/80 MHz bandwidth enabling the use
of higher data rates, lower MAC delay due to faster transmission of the
data, and better fairness between different contending STAs. It also to
be noted that FIGS. 6a and 6b illustrate contention between STAs of the
same AC. The present features may be applied also for contention between
STAs of different ACs. Let us now further study some example embodiments
in more detail.

[0052] Bandwidth-Dependent TXOP Limit Definition

[0053] FIGS. 7 and 8 illustrate an embodiment by which bandwidth-dependent
TXOP limit parameters may be co-ordinated and provided for TXOP holders
in a network.

[0054]FIG. 7 illustrates features of an entity providing information on
TXOP limits for TXOP holders. For example, the features of FIG. 7 may be
applied in the AP 20, such as an IEEE 802.11ac WLAN access point.

[0055] At least one set of transmission opportunity limit parameters, each
of the parameters being associated with specific bandwidth, is retrieved
or computed 700. Thus, an AP 20 may apply predefined TXOP limit parameter
values, or dynamically alter the TXOP parameter values e.g. on the basis
of current load situation. The AP 20 may also consider the amount of
overlapping further APs in its operating channels and reduce the use of
overlapping channels to improve the co-existence of the networks. The AP
may also receive the channel specific TXOP limit parameter values from a
central unit that is mastering the performance and load balancing of the
local area network.

[0056] It will be appreciated that there may be multiple sets of
bandwidth-specific TXOP limit parameters, e.g. for each IEEE 802.11e AC
to differentiate traffic flows with different QoS requirements. The
set(s) of bandwidth-specific TXOP limit parameters are sent 710 to one or
more radio devices.

[0057]FIG. 8 illustrates features for an entity capable of operating as a
multi-channel TXOP holder, such as the device 10 which may operate as an
IEEE 802.11ac STA. A set of bandwidth-specific TXOP limit parameters is
received 800 and stored in memory. The set may be received from the AP 20
applying the features of FIG. 7, for example.

[0058] When there is a need to transmit and define properties of a TXOP,
the stored TXOP limit information may be retrieved, e.g. after detecting
810 information on available channels and bandwidth.

[0059] A TXOP limit is set 820 for the primary channel for a TXOP. In one
example embodiment, a value for this primary channel TXOP limit is
obtained from the "TXOP Limit" field 900 of the AC-specific EDCA
parameter record 900 illustrated in FIG. 9.

[0060] In the example embodiment of FIG. 8, a TXOP limit may then be
defined for each available secondary channel on the basis of the set of
bandwidth-specific TXOP limit parameters and the TXOP limit of the
primary channel. Thus, referring also to the example of FIG. 4, a TXOP
limit value is defined for a secondary channel on the basis of a TXOP
parameter associated in the set with bandwidth available by the
respective secondary channel for the TXOP. For example, in case the
Secondary channel of FIG. 4 is available, 40 MHz bandwidth is available
and the TXOP limit value for the secondary channel is calculated on the
basis of the TXOPLimit40. These channel-specific TXOP limit values may
then be applied for controlling occupancy of the respective channels,
e.g. as already indicated in connection with FIG. 5. In an example
variation of FIG. 8, the TXOP limits for secondary channels are not
dependent on the TXOP limit of the primary channel.

[0061] In an example embodiment, a new information element is specified
for bandwidth-specific TXOP limit parameter information. As illustrated
in the example element 100 of FIG. 10a, the information element may
specify bandwidth-specific TXOP Limits parameter set 102a-d for each AC.
FIG. 10b illustrates an example of contents of such parameter set 102.
FIG. 10c depicts the access category identifier (ACI) field 104
indicating the AC and 10d the coding of the ACI value field 112.

[0062] As illustrated in FIG. 10b, the parameter set 102 may comprise
bandwidth-specific factor values 106, 108, 110, in this example for 40
MHz band, 80 MHz band and 160 MHz band, respectively. Each of the factor
values may be unsigned integer. The actual channel-specific TXOP limit
values may then be calculated (510, 830) on the basis of these factor
values and the TXOP limit of the primary channel.

[0063] For example, the value of 40 MHz factor 106 may be divided by 255
and multiplied by the duration of the TXOPLimit (representing the TXOP
limit of the primary channel) to calculate the TXOPLimit40. A reference
is also made to FIG. 4 illustrating such TXOP limit 402. This limits the
medium occupancy of the 40 MHz or wider bandwidth transmissions. Value 0
in 40 MHz Factor may indicate that no transmission shall use 40 MHz or
wider bandwidth. The value of 80 MHz factor 108 may be divided by 255 and
multiplied by the duration of the TXOPLimit to calculate the TXOPLimit80
404 that limit the medium occupancy of the 80 MHz or wider transmissions.
Value 0 in 80 MHz Factor may indicate that no transmission shall use 80
MHz or wider bandwidth. The value of 160 MHz Factor may similarly be
divided by 255 and multiplied by the duration of the TXOPLimit to
calculate the TXOPLimit160 that limits the medium occupancy of the 160
MHz or wider transmissions. Value 0 in 160 MHz Factor may be set to
indicate that no transmission shall use 160 MHz bandwidth. The TXOP limit
values may be rounded up to next multiple of 32 micro seconds.

[0064] In some embodiments there is no differentiation between ACs and a
single set of TXOP limit parameters may be transmitted 710 and applied
830 by the device 10. FIG. 10e illustrates a further example information
element 114 which may be used to deliver in such case. The information
element comprises an element identifier, length information, and fields
for bandwidth-specific factors.

[0065] The QoS capable AP 20 may be arranged to transmit (710) the
bandwidth-specific TXOP limit parameter sets 100, 114 at the same time as
the AC-specific EDCA parameter sets illustrated in FIG. 9. Thus, the AP
20 may be arranged to include the bandwidth-specific TXOP limit parameter
sets 100 in Beacon frames, Probe Response frames, and (Re)Association
Response frames by inclusion of a new information element comprising the
bandwidth-specific TXOP limit parameters, e.g. by applying the example
information element 100, 114. However, in an alternative embodiment the
EDCA parameter set information element is modified to comprise the
bandwidth-specific TXOP limit parameters. If no (applicable)
bandwidth-specific TXOP limit parameters are received, the STA 10, 30 may
be arranged to use a default TXOP limit value for the primary channel, or
calculate bandwidth-dependent TXOP limit value(s) independently.

[0066] This embodiment enables to have compatibility with already
specified EDCA parameters. The channel-specific TXOP limits can be used
in conjunction with different AC specific EDCA parameters. It is to be
noted that two different modes of operation are enabled: (i) channel
specific TXOP limits with same EDCA parameters where service
differentiation is controlled only by TXOP limits (airtime); and (ii)
channel specific TXOP limits with different EDCA parameters where service
differentiation is controlled by both TXOP limit (airtime) and AC
specific EDCA parameters (prioritized channel access). Furthermore, the
channel usage may be coordinated more specifically and in overlapping
basic services set (OBSS) situations it becomes possible to tune the
network performance more precisely.

[0067] Bandwidth-Dependent TXOP Parameter Calculation Examples

[0068] In one example, the TXOP limit of a STA i on channel
jε[primary,secondary,tertiary,quaternary] may be computed (510)
as the minimum of time required by the STA to transmit all MAC service
data units (MSDUs) in its queue and time of a default AC's TXOP limit
TX0Plim[AC] given by

[0069] where [0070] k=number of MSDUs in the STA's queue, [0071]
Lik[AC]=length of MSDU in a specific AC, [0072] Rj=PHY
data rate of primary channel in bps, [0073] O=physical layer (PHY) and
MAC protocol overheads including duration of the interframe space and to
transmit acknowledgment frames in time units.

[0074] The example expression (1) assigns the TXOP limit according to the
load requirement of STAi up to the maximum duration allowed by the
default TXOP limit of a specific AC. This ensures that no excess TXOP
limit is assigned should the default TXOP limit of different ACs be
non-optimal.

[0075] It is to be noted that the expression (1) can be readily replaced
by some other TXOP limit calculation algorithm, which aims to allocate
different airtimes for STAB with different QoS profiles based on some
fairness criteria. Further, it is to be noted that the expected TXOP
duration may be calculated (520) by applying an equation similar to (1).

[0076] In some example embodiments, common factor based TXOP limits are
applied. A bandwidth increment factor f reflecting the ratio of total
available bandwidth and the bandwidth of the primary channel may be
applied to calculate the TXOP limit values. The bandwidth increment
factor f can be simply expressed as

[0081] This enables to limit the transmission time of any given data
frames by the bandwidth increment factor f should multi-channel operation
be possible.

[0082] The calculated expected TXOP duration value (based on
channel-specific TXOP limits or a common factor) may then be applied to
define the duration of the TXOP. In case of IEEE802.11e based WLAN, a STA
may initiate multiple frame exchange sequences to transmit MMPDUs and/or
MSDUs within the same AC during an EDCA TXOP won by an EDCA function
(EDCAF) of the STA.

[0083] The TXOP duration value may be sent for other radio devices to
indicate the channel occupancy. In the embodiment applying IEEE 802.11
features, the calculated duration of the TXOP is included in a duration
field of a request to send (RTS) message. This enables network allocation
vector (NAV) protection on secondary channels for primary users and is
fully compatible with existing 802.11 systems. Protection against hidden
terminals on secondary channels may thus be achieved without incurring
additional signaling overheads for explicit channel reservation and
relinquishment.

[0084] FIG. 11 illustrates examples of common factor based TXOP limits,
where the TXOP limits 118a, 118b, 118c for the secondary channels are
calculated on the basis of the TXOP limit 116 of the primary channel by
expression (3).

[0085] Medium Occupancy During TXOP

[0086] As already indicated, the total TXOP duration may be estimated on
the basis of measurements (530) during a TXOP by at least one counter.
Below some example embodiments are provided for arranging the measurement
(530) and ensuring (540) that the channel-specific TXOP limit values are
not exceeded.

[0087] In some embodiments, single duration measurement is applied. Thus,
the TXOP holder uses (530) a single counter when estimating the total
duration of a TXOP. The total TXOP duration value may be incremented
whenever the sum of elapsed duration and the future estimated remaining
duration increases, regardless of transmission bandwidth. However, during
the TXOP the TXOP holder ensures (540) that a specific channel may be
occupied only if the total TXOP duration does not exceed the TXOP limit
of the specific channel. If the total TXOP duration is larger than a TXOP
limit value of a particular channel then during the TXOP that channel may
no longer have NAV protection for TXOP holder and the channel may not
transmit frames that belong to the TXOP.

[0094] This scenario is also illustrated in FIG. 12a. The TXOP holder may
occupy only the bandwidths of 20 and 40 MHz (primary and secondary
channels), but not the bandwidth of 80 MHz (tertiary and quarternary
channels) as the measured TXOP duration has exceeded the TXOP limit of
the tertiary and quaternary channels. The use of 160 MHz bandwidth is
restricted by the value 0 of TXOPLimit160.

[0101] This scenario is also illustrated in FIG. 12b. Now, the TXOP holder
may now occupy the bandwidth of 20, 40, and 80 MHz (primary, secondary,
tertiary, and quaternary channels) as the used TXOP duration has not
exceeded any channel's TXOP limits. The use of 160 MHz bandwidth is
restricted by the value 0 of TXOPLimit160. An advantage of this scheme
lies in the simplicity of measurement of medium occupancy within TXOP,
i.e. it may be implemented with just a single counter 120.

[0102] FIG. 13 illustrates bookkeeping of the TXOP duration in case of
single duration measurement. In this example data are first transmitted
on the primary channel, and then also the three secondary channels are
reserved by the RTS/CTS signalling. The total TXOP duration may be
increased 130 whenever the sum of elapsed and future estimated remaining
durations increase, regardless of transmission bandwidth.

[0103] In some other example embodiments, the TXOP holder maintains
multiple counters to enable estimation of the total TXOP duration and
determines the total TXOP duration according to bandwidth occupancy.
Thus, duration of the bandwidth occupancy may be measured for two or more
combinations of channels. In one example for systems with 8 available
channels, the following combinations of channels may be measured:
[0104] A. Measure the duration when TXOP holder occupies the primary
channel [0105] B. Measure the duration when TXOP holder occupies the
secondary channel [0106] C. Measure the duration when TXOP holder
occupies the tertiary and quarternary channels [0107] D. Measure the
duration when TXOP holder occupies the quinary (5), senary (6), septenary
(7), and octonary (8) channels

[0108] In the example of FIG. 14a, the transmission in 160 MHz means that
the total TXOP durations of all primary (A), secondary (B), tertiary and
quaternary (C), as well as quinary (5), senary (6), septenary (7), and
octonary (8) (D) channels may be incremented 140.

[0109] Similarly, as illustrated in FIG. 14b, the transmission in 40 MHz
bandwidth means that only the total TXOP durations of the primary (A) and
secondary (B) channels may be incremented 142, but the total TXOP
durations of the tertiary and quarternary (C), and quinary (5), senary
(6), septenary (7), and octonary (8) (D) channels are not incremented.

[0110] Accordingly, the following rules may be applied for
bandwidth-specific TXOP limits: [0111] A. The duration when TXOP holder
occupies the primary channel shall not exceed the TXOPLimit. [0112] B.
The duration when TXOP holder occupies the secondary channel shall not
exceed the TXOPLimit40. [0113] C. The duration when TXOP holder occupies
the tertiary and quarternary channels shall not exceed the TXOPLimit80.
[0114] D. The duration when TXOP holder occupies the quinary (5), senary
(6), septenary (7), and octonary (8) channels shall not exceed the
TXOPLimit160.

[0115] These rules may be applied by the EDCAF to limit the wireless
medium occupancy for each AC.

[0116] This embodiment facilitates flexibility of bookkeeping. The use of
multiple counters enables the use of wider bandwidth later than just at
the beginning of a TXOP, i.e. the transmission to larger bandwidth may be
performed at any time during the TXOP. The total TXOP duration of options
A, B, C and D is set for duration that the channel is occupied. With
reference to the example of FIG. 13, when multiple timers are applied,
the total TXOP duration of only the primary channel may be incremented at
example point of time 132, and the total TXOP durations of all of used
channels are incremented at point 134.

[0117]FIG. 15 provides a further example of TXOP duration bookkeeping
when multiple duration measurements are performed and the RTS CTS
signaling is not capable to reserve to requested bandwidth completely.
The 80 MHz bandwidth is occupied until the transmission of the CTS reply
is started 152. During the medium occupancy for RTS transmission and the
following SIFS, the total TXOP durations for 20, 40, and 80 MHz are
incremented 150. During the CTS and data transmissions, 40 MHz bandwidth
is occupied and hence only the total TXOP durations for 20 and 40 MHz are
incremented 154, i.e. the NAV protection is not established for the whole
80 MHz bandwidth.

[0118]FIG. 16 provides a further example of TXOP duration bookkeeping
when multiple duration measurements are performed. The NAV is set by the
RTS/CTS for the entire 80 MHz bandwidth. Although the TXOP holder uses
only 40 MHz bandwidth for data exchange, the total TXOP durations for 20,
40 and 80 MHz are set for the duration 160, since all four channels are
considered reserved for the TXOP holder.

[0119] In a still further example, in some cases an entity other than the
TXOP holder, such as the AP 20 or a receiving entity, may be arranged to
carry out at least some of the above illustrated features related to
determining TXOP properties and channel occupancy duration on the basis
of the bandwidth available for the TXOP. For example, the AP 20 may be
arranged to adapt TXOP limits on the basis of the available bandwidth.
Similarly, the AP 20 may monitor the behaviour of the devices 10, 30. If
a device does not follow the channel specific TXOP limits, the AP 20 may
disassociate the device and stop the data service.

[0120]FIG. 17 is a simplified block diagram of high-level elements of an
apparatus according to an embodiment. The apparatus comprises a data
processing element DP 170 with at least one data processor and a memory
178 storing a program 180. The apparatus may comprise at least one radio
frequency transceiver 172 with a transmitter 176 and a receiver 174.

[0121] The memory 178 may comprise a volatile portion and non-volatile
portion and implemented using any suitable data storage technology
suitable for the technical implementation context of the respective
entity. The data processing element 170 may be of any type suitable to
the local technical environment, and may include one or more of general
purpose computers, special purpose computers (such as an
application-specific integrated circuit (ASIC) or a field programmable
gate array FPGA), microprocessors, digital signal processors (DSPs) and
processors based on a multi-core processor architecture, as non-limiting
examples.

[0122] In general, various embodiments of the presently disclosed features
may be implemented by computer software stored in a computer-readable
medium, such as the memory 178 and executable by the data processing
element 170 of the apparatus, or by hardware (such as an ASIC), or by a
combination of software and/or firmware and hardware in the apparatus.

[0123] In the context of this document, a "computer-readable medium" may
be any media or means that can contain, store, communicate, propagate or
transport the instructions for use by or in connection with an
instruction execution system, apparatus, or device, such as a computer,
with one example of a computer described and depicted in FIG. 17. A
computer-readable medium may comprise a computer-readable storage medium
that may be any media or means that can contain or store the instructions
for use by or in connection with an instruction execution system,
apparatus, or device, such as a computer.

[0124] The program 180 may comprise computer program instructions that,
when executed by a data processor 170, enable the apparatus to operate in
accordance with at least some embodiments of the present invention. The
program may comprise computer program code configured to, with the at
least one processor, cause the apparatus to perform at least some of the
features illustrated in connection with FIGS. 3 to 16.

[0125] The apparatus could be in a form of a chip unit or some other kind
of hardware module for controlling a radio device. The hardware module
may form part of the device and could be removable. Some examples of such
hardware module include a sub-assembly or an accessory device.

[0126] The apparatus of FIG. 17 may be arranged to use licensed and/or
unlicensed bands. The apparatus may be arranged to support MIMO or
multi-user MIMO and comprise a plurality of antennas and transceivers.
The apparatus may be embodied as a mobile communications device. For
instance, a mobile communications device such as the device 10, 30 of
FIG. 1 may comprise the elements of FIG. 17. The apparatus may be
configured to operate as an IEEE 802.11ac STA, AP, or mesh point. The
apparatus is configured to arrange an EDCAF for each AC contending for
TXOPs applying at least some of the above illustrated features. It should
be appreciated that the above-illustrated embodiments provide only
examples of some radio technologies in which the features related to
applying adaptive transmission opportunity properties may be applied.
However, in some other embodiments, the apparatus may operate according
to a different communication protocol to the IEEE WLAN 802.11 protocols.
It will be appreciated that the apparatus may comprise various further
elements, such as further processor(s), further communication unit(s),
user interface components, a battery, a media capturing element, and a
user identity module, not discussed in detail herein.

[0127] Although the apparatus and the data processing element 170 are
depicted as a single entity, different features may be implemented in one
or more physical or logical entities. There may be further specific
functional module(s), for instance for carrying one or more of the
features described in connection with FIG. 3, 5, 7, or 8.

[0128] If desired, at least some of the different functions discussed
herein may be performed in a different order and/or concurrently with
each other. Furthermore, if desired, one or more of the above-described
functions may be optional or may be combined.

[0129] Although various aspects of the invention are set out in the
independent claims, other aspects of the invention comprise other
combinations of features from the described embodiments and/or the
dependent claims with the features of the independent claims, and not
solely the combinations explicitly set out in the claims.

[0130] It is also noted herein that while the above describes example
embodiments of the invention, these descriptions should not be viewed in
a limiting sense. Rather, there are several variations and modifications
which may be made without departing from the scope of the present
invention as defined in the appended claims.